Method for producing cyclohexane dicarboxylic acids and the derivatives thereof

ABSTRACT

The invention relates to a process for preparing cyclohexanedicarboxylic acids or derivatives thereof, such as esters and/or anhydrides, encompassing the reaction of diene/maleic acid anhydride mixtures, in particular of butadiene/maleic acid anhydride mixtures or of mixtures of maleic acid anhydrides and C5-dienes to give alkyl-substituted or unsubstituted cyclohexenedicarboxylic acid anhydrides in the condensed phase, ester formation, and then hydrogenation to give the corresponding cyclohexanedicarboxylic acid derivative, and also to the use of the cyclohexanedicarboxylic acids or derivatives thereof prepared according to the invention as plasticizers for plastics.

[0001] The invention relates to a process for preparingcyclohexanedicarboxylic acids or derivatives thereof, such as estersand/or anhydrides, encompassing the reaction of diene/maleic acidanhydride mixtures, in particular of butadiene/maleic acid anhydridemixtures or of mixtures of maleic acid anhydride and at least oneC5-diene to give alkyl-substituted or unsubstitutedcyclohexanedicarboxylic acid anhydrides in the condensed phase.

[0002] The invention further relates to the alkyl-substituted orunsubstituted cyclohexanedicarboxylicacids or derivatives thereof,mixtures, comprising one or more thereof, made in accordance with theinvention as well as the use of the reaction products prepared accordingto the invention, i.e. of the resultant alkyl-substituted orunsubstituted cyclohexanedicarboxylic acid compounds, in particular ofthe cyclohexanedicarboxylic esters, as plasticizers in plastics, inparticular for polyvinyl chloride (PVC) and polyvinyl butyral (PVB).

[0003] Phthalates, e.g. dibutyl, dioctyl, or diisononyl phthalates havehitherto been used very frequently as plasticizers in plastics, such asPVC, as is apparent from FR-A 23 97 131. However, they have recentlybeen alleged to be hazardous to health, and their use in plastics, forexample in toy production, is subject to increasing criticism and hasnow been forbidden in some countries. Experiments on animals have nowshown that phthalates can cause peroxisome proliferation, which is acause of the liver tumors arising in long-term studies on mice and rats.

[0004] The use of some cyclohexane-1,2-dicarboxylic esters asplasticizers is likewise known from the prior art. For example, the useof dimethyl or diethyl cyclohexanedicarboxylates (DE-A 28 23 165) anddi-2-ethylhexyl cyclohexane-1,2-dicarboxylate (DE-A 12 63 296) asplasticizers in plastics has been described.

[0005] PCT/EP 98/08346 discloses that cyclohexanepolycarboxylic acidsand derivatives thereof can be used as plasticizers. In this connectionit is disclosed that the density and viscosity ofcyclohexanepolycarboxylic acids and derivatives thereof is lower thanthat of the phthalates mainly used as plasticizers hitherto, andmoreover that these compounds lead, inter alia, to betterlow-temperature flexibility of the plastic when comparison is made withthe use of the corresponding phthalates as plasticizers. PCT/EP 98/08346also discloses that the dry-blend processing performance ofcyclohexanepolycarboxylic acids and derivatives thereof is better thanthat of the corresponding phthalates and these compounds therefore haveadvantages in terms of increased production speed, and also in plastisolprocessing, via markedly lower viscosity.

[0006] EP-A 0 603 825 relates to a process for preparingcyclohexane-1,4-dicarboxylic acid by hydrogenating terephthalic acidwith use of a supported palladium catalyst, the support used beingaluminum oxide, silicon dioxide, or activated charcoal.

[0007] DE-A 199 77 977.2 discloses the use, as a plasticizer forplastics, of a cyclohexanepolycarboxylic acid or of a derivativethereof, where this brings about no biologically significant peroxisomeproliferation, i.e. is regarded as toxicologically non-hazardous.

[0008] DE-A 199 27 978.0 relates to selected cyclohexane-1,3- and-1,4-dicarboxylic esters which are prepared by hydrogenation of thecorresponding isophthalic and terephthalic esters, by way of contactwith a hydrogen-containing gas in the presence of a catalyst having, asactive metal, at least one metal of the 8th transition group of theperiodic table of the elements, on its own or together with at least onemetal of the 1st or 7th transition group of the periodic table of theelements, applied to a support. The use as plasticizer is likewisementioned.

[0009] In principle, chosen di-esters of norbonan-2,3-dicarboxylic acid,4-methylcyclohexane-1,2-dicarboxylic acid and3-methylcyclohexane-1,2-dicarboxylic acid are known, e.g. from JP2000-034492, JP 70-11074, JP 71-73342, JP 52-95025 or JP 71-38205.Methylcyclohexane-1,2-dicarboxylic acid esters on basis of alcohols with6 to 28 C atoms are until now only described as plasticizers forpolyolefins, e.g. in JP 63-06252. Merely esters ofnorbonan-2,3-dicarboxylic acid with n-octanol or 2-ethylhexanol asalcohol component have been described for PVC (S. Matsuda, S. Kikkawa,Kogyo Kagaku Zasshi (1959) 62, 1838-1841).

[0010] The use of toxicologically non-hazardous plasticizers isparticularly important for plastics used for producing articles foreveryday use. Polyvinyl chloride, in particular, is used to produce manyarticles in daily use, including children's toys.

[0011] All of the processes utilized hitherto for preparing thecyclohexanecarboxylic acid derivatives are based on the hydrogenation ofthe underlying phthalic esters. This adds a stage to the reaction toprepare the plasticizers and makes the product more expensive.

[0012] It is an object of the present invention, therefore, in the firstinstance to provide a process which can prepare alkyl-substituted orunsubstituted cyclohexanedicarboxylic acids or derivatives thereof andwhich uses low-cost raw materials which are readily available in largequantities.

[0013] We have found that this object is achieved by means of a processfor preparing an alkyl-substituted or unsubstitutedcyclohexanedicarboxylic acid or a derivative thereof, encompassing thefollowing sequences of steps (1) to (3):

[0014] (1) Converting a diene/maleic acid anhydride mixture to givealkyl-substituted or unsubstituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0015] (2) Forming an ester from an alkyl-substituted or unsubstitutedcyclohexenedicarboxylic acid anhydride;

[0016] (3) Hydrogenation of the alkyl-substituted or unsubstitutedcyclohexene derivative of step (2) to give the corresponding derivativeof cyclohexane; or

[0017] (1) Converting a diene/maleic acid anhydride mixture to give analkyl-substituted or unsubstituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0018] (3) Hydrogenation of the alkyl-substituted or unsubstitutedcyclohexenedicarboxylic acid anhydride to give cyclohexanedicarboxylicanhydride;

[0019] (2) Forming an ester from the alkyl-substituted or unsubstitutedcyclohexanedicarboxylic acid anhydride.

[0020] Therein and in the framework of the present invention, analkyl-substituted cyclohexanedicarboxylic acid anhydride is acyclohexane derivative with an alkyl substituent on the aliphatic ringor also a cyclohexane derivative, bridged with an alkyl residue, i.e. abicyclical structure.

[0021] Within the framework of the present invention it is preferred ifthe cyclohexanedicarboxylic acid is unsubstituted or provided with amethyl substituent. In accordance with the invention, the methylsubstituent may also be a methylene bridge.

[0022] Dienes are preferably dienes with less than 10 carbon atoms, inparticular less than 6 carbon atoms, particularly preferably butadieneor dienes with 5 carbon atoms. Dienes appropriate in accordance with theinvention are dienes with conjugated double bonds. Dienes with isolateddouble bonds do not react under the reaction conditions of theinvention.

[0023] Thus, in a particularly preferred embodiment of the presentinvention, the invention relates to a process for preparing acyclohexanedicarboxylic acid or a derivative thereof, encompassing thefollowing sequences of steps (1) to (3):

[0024] (1) Converting a butadiene/maleic acid anhydride mixture to givecyclohexenedicarboxylic acid anhydride in the condensed phase;

[0025] (2) Forming an ester from a cyclohexenedicarboxylic acidanhydride;

[0026] (3) Hydrogenation of the cyclohexene derivative of step (2) togive the corresponding derivative of cyclohexane; or

[0027] (1) Converting a butadiene/maleic acid anhydride mixture to givecyclohexenedicarboxylic acid anhydride in the condensed phase;

[0028] (3) Hydrogenation of the cyclohexenedicarboxylic acid anhydrideto give cyclohexanedicarboxylic acid anhydride;

[0029] (2) Forming an ester from the cyclohexanedicarboxylic acidanhydride.

[0030] The advantage of this process is the use of a crude maleic acidanhydride solution and a crude butadiene mixture for the reaction ofstep (1), where these comprise by-products and inert constituents, suchas nitrogen, oxygen, or n- or isobutanes, and therefore the saving ofone work-up step for obtaining pure butadiene and pure maleic anhydride.

[0031] In another preferred embodiment, the present invention relates toa process for preparing an alkyl-substituted cyclohexanedicarboxylicacid or a derivative thereof, comprising the following sequence of steps(1) to (3):

[0032] (1) Converting a mixture of maleic acid anhydride and at leastone C5 diene to give an alkyl-substituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0033] (2) Forming an ester from the alkyl-substitutedcyclohexenedicarboxylic acid anhydride;

[0034] (3) Hydrogenation of the alkyl-substituted cyclohexene derivativeof step (2) to give the corresponding derivative of cyclohexane; or

[0035] (1) Converting a mixture of maleic acid anhydride and at leastone C5 diene to give an alkyl-substituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0036] (3) Hydrogenation of the alkyl-substitutedcyclohexenedicarboxylic acid anhydride to give cyclohexanedicarboxylicacid anhydride;

[0037] (2) Forming an ester from the alkyl-substitutedcyclohexanedicarboxylic acid anhydride.

[0038] According to the present invention, “cyclohexanedicarboxylicacids and derivatives thereof” encompass the respectivecyclohexanedicarboxylic acids themselves and also derivatives thereof,and particular mention should be made of mono- or diesters, and alsoanhydrides, of the cyclohexanedicarboxylic acids. The esters used arealkyl, cycloalkyl, and also alkoxyalkyl esters, where the alkyl,cycloalkyl, and alkoxyalkyl groups generally encompass from 1 to 30carbon atoms, preferably from 2 to 20 carbon atoms, and particularlypreferably from 3 to 18 carbon atoms, and may be branched or linear.

[0039] Suitable crude butadiene mixtures are butadiene-containingmixtures composed predominantly of hydrocarbons, the hydrocarbons otherthan butadiene being inert under the conditions of step (1) of theprocess.

[0040] Examples of these inert hydrocarbons are alkanes, monoalkenes,cycloalkanes, benzene, and dialkylbenzenes, for example propane,n-butane, 2-methylpropane, 1-butene, cis-2-butene, trans-2-butene,isobutene, cyclohexane, benzene, toluene and the xylenes.

[0041] There is generally no lower limit on the proportion of butadienein this crude butadiene mixtures, but, for example for reasons ofspace-time yield in step (1) of the process, it is generally desirablefor the butadiene content in these mixtures to be as high as possible.Another factor which can control the content of butadiene in the crudebutadiene mixture is the intended makeup of the hydrocarbon streamremaining after stage (1) of the process: For example, if the intentionis that the hydrocarbon stream be practically free from butadiene afterthe reaction of step (1) of the process, the content of butadiene in themixture used should be adjusted correspondingly.

[0042] These crude butadiene mixtures preferably comprise from 20 to 95%by weight, in particular from 40 to 50% by weight, of butadiene.

[0043] A particularly low-cost crude butadiene mixture is what is knownas the crude C₄ cut, whose butadiene content is generally from 40 to 50%by weight. This cut is produced industrially in large quantities (cf.,for example, K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie,VCH Weinheim, 5th edition, 1998, and also FR-A 1 343 169, DE-A 14 43 362and DE-A 14 68 843). Using the crude C₄ cut it is possible to carry outstep (1) of the process in such a way that the resultant hydrocarbonstream is practically butadiene-free. The makeup of this hydrocarbonstream is the same as that of what is known as raffinate I, which isnormally obtained by other methods of butadiene extraction from the C₄cut from crackers, and this stream can therefore be used as areplacement for raffinate I.

[0044] As is well known, the formation of azeotropes with otherconstituents of the C₄ cut generally makes it impossible to usedistillation to separate butadiene from C₄ cuts, and complicated methodsare therefore usually needed to extract the butadiene from these C₄cuts.

[0045] Stage (1) of the process on its own therefore also provides anovel process for removing butadiene from butadiene-containinghydrocarbon mixtures, and in particular from C₄ cuts (cf. K. Weissermel,H.-J. Arpe, Industrielle Organische Chemie, VCH Weinheim, 5th edition,1998).

[0046] Thus, method step (1) of the present invention is also a processfor the separation of butadiene from butadiene-containing hydrocarbonflows, wherein the hydrocarbon flow is reacting with maleic acidanhydride and the resultant cyclohexene-dicarboxylic acid anhydride isseparated from the remaining hydrocarbon flow.

[0047] In one preferred embodiment of the invention, thebutadiene/maleic acid anhydride mixture for the reaction according tostep (1) is obtained by a process comprising the oxidation of streamscomprising n-butene or butadiene or a mixture thereof.

[0048] For the purposes of the present invention, the preferredbutadiene used is 1,3-butadiene. In accordance with the invention, thebutadiene/maleic acid anhydride mixture for the reaction according tostep (1) may however also be obtained by a process comprising theoxidation of flows containing n-butane.

[0049] For the purposes of the present invention, streams comprisingn-butene or butadiene or a mixture thereof are preferably a C₄ fractionof a raffinate stream. Examples of these are mixtures with the followingmakeup: butane from 10 to 90% by weight, butene from 10 to 90% byweight, where the butene fraction may have the following makeup: from 0to 100% by weight, in particular from 0 to 80% by weight, particularlypreferably from 0 to 50% by weight, of 1-butene, from 0 to 100% byweight, in particular from 0 to 80% by weight, particularly preferablyfrom 0 to 50% by weight, of cis-2-butene, from 0 to 100% by weight, inparticular from 0 to 80% by weight, particularly preferably from 0 to50% by weight, of trans-2-butene, from 0 to 10% by weight of isobutene,and it is possible here that the stream also comprises small amounts,for example from 0 to 20% by weight, in particular from 0 to 10% byweight, of other hydrocarbons, in particular C₅ hydrocarbons. It ismoreover also possible to use the pure n-butene or a mixture of a puren-butene and butadiene.

[0050] A particularly preferred starting material used is that known asraffinate II, i.e. an n-butene-containing C₄ hydrocarbon mixture, asobtained from the C₄ cut of crackers after separating off most of theisobutene. However, removal of any butadiene also present is not anessential requirement of the process of the invention. There istherefore no need for a further purification step.

[0051] For the purposes of the present invention, use is in particularmade of n-butene-rich streams which comprise at least 60% by weight, inparticular at least 80% by weight, of n-butene and relatively smallamounts of n- and isobutane and other hydrocarbons.

[0052] Substantial control of the oxidation of streams comprisingn-butene or butadiene or a mixture therefore can be achieved by way ofthe use of various catalysts and the selection of the reactionconditions.

[0053] According to the invention, an example of the process used forobtaining the butadiene/maleic acid anhydride mixture for the reactionof step (1) comprises the oxidation of n-butene to give butadiene.According to the invention it is possible for this oxidation to befollowed by addition of maleic acid anhydride (MA) to the crudebutadiene in order to obtain a butadiene/maleic acid anhydride mixturefor the reaction of step (1).

[0054] In one preferred embodiment, the present invention provides aprocess for preparing a cyclohexanedicarboxylic acid or a derivativethereof, which proceeds according to the following scheme (I):

[0055] wherein in scheme (I) E is n-butenes (raffinate), L is air, cat Ais catalyst system A, cat B is catalyst system B, and P iscyclohexane-1,2-dicarboxylic ester.

[0056] Steps (1) to (3) of the process of the invention are indicated inthe reaction scheme here, and also within the reaction schemes whichfollow.

[0057] The reaction of butenes on a catalyst system A (cat A), forexample a catalyst whose makeup is (Fe, Co)—Mo—O+Bi—W—O, to givebutadiene can be carried out with high butadiene yields of from 85 to90%. U.S. Pat. No. 4,595,788 and U.S. Pat. No. 4,547,615 describeprocesses for preparing butadiene or conjugated diolefins. Butadiene isobtained in yields of more than 80% by using molybdenum-, bismuth-, ornickel-based catalysts in the reaction of C4 mixtures comprisingn-butene. As has been shown by comparative experiments, these reactionsalso give small amounts of maleic acid anhydride (from 1 to 10%)alongside butadiene.

[0058] Since the butadiene is used for the reaction of step (1), MAcontent in the butadiene is not disruptive. It enables thedehydrogenation to obtain butadiene as raw material for the subsequentreaction to be operated in a particularly cost-effective manner withhigh butene conversion and incorporating an additional yield of MA, forexample by the process of reaction scheme (III).

[0059] In one preferred embodiment of the invention, the n-butene toprepare the butadiene/maleic acid anhydride mixture is obtained by aprocess comprising the oxidation of flows containing n-butane.

[0060] It is also possible to start from linear butenes orbutene-containing starting materials to obtain mixtures of butadiene andMA in suitable ratios of mixing.

[0061] The invention therefore also provides a process for preparing acyclohexanedicarboxylic acid or a derivative thereof, where thebutadiene/maleic acid anhydride mixture for the reaction according tostep (1) is obtained by a process comprising the oxidation of n-buteneto give a butadiene/maleic acid anhydride mixture.

[0062] In another preferred embodiment, the invention provides a processfor preparing a cyclohexanedicarboxylic acid or a derivative thereof,which proceeds according to the following scheme (II):

[0063] wherein in scheme (II) E is n-butenes (raffinate), L is air, catC is catalyst system C, and P is cyclohexane-1,2-dicarboxylic ester.

[0064] This catalyst system C (cat C) is a catalyst system suitable forcatalyzing the reaction of n-butenes to give a butadiene/maleic acidanhydride mixture.

[0065] The crude mixture of MA and butadiene may then be reacted in step(1) in a high-boiling, inert solvent used as absorption medium for theMA.

[0066] Mixtures of maleic acid anhydride (MA) and the butadieneintermediate can be obtained under mild reaction conditions by oxidizingunsaturated n-C4 hydrocarbons on a variety of heterogeneous catalysts.Suitable balance of reaction conditions and catalyst permit thebutadiene and MA to be obtained. An example of a description of suitableconditions and catalysts is found in K. Weissermel, H.-J. Arpe,“Industrielle Organische Chemie”, 4th edition, 1994, VCH Weinheim.

[0067] The further reaction of butadiene to give maleic acid anhydridetakes place on a second catalyst system B (cat B), for exampleSbMo_(3.06)Ti_(0.6)Nb_(0.1)Sn_(0.8)O_(x)/TiO₂. Any maleic acid anhydridepresent in the feed is not disruptive and continues to be present,without decomposition, in the product stream. High overall yields cantherefore be obtained by using stages in which butene is reacted on afirst catalyst system A to give butadiene and then reacted on a secondcatalyst system B, and the ratio of butadiene and MA in the productstream can therefore be adjusted.

[0068] By way of example, DE 28 13 424 describes suitable conditions forthe oxidation of butadiene to give maleic anhydride, using catalystscomprising oxides of antimony and molybdenum.

[0069] MA is obtained in the form of a crude solution from the reactoreffluent by absorption in a high-boiling inert solvent. The absorptiontemperature is preferably above 55° C. in order to avoid crystallizationof MA (melting point 55° C.). There is hardly any absorption oflower-boiling components (butadiene, by-products, water of combustion,carbon dioxide), and these components can readily be recovered from theexhaust gas, for example by pressure-swing absorption/temperature-swingabsorption (PSA/TSA).

[0070] In contrast to industrial processes for MA preparation from C4hydrocarbons, this stream is not, however, used as feed to the gas-phaseoxidation to increase MA yield. Instead, for the purposes of the presentinvention, the crude mixture of the low boilers, which predominantlycomprises butadiene, and also comprises other olefins and butanes, is asuitable raw material for the reaction of step (1), which is aDiels-Alder reaction with the crude MA solution. The crude mixture canbe reacted with MA in the inert solvent used for MA absorption. TheDiels-Alder product obtained is cyclohexanedicarboxylic acid anhydride.Suitable conditions for carrying out the reaction of step (1) are givenby way of example in “Organic Syntheses”, Coll. Vol. IV, 1963, J. Wiley& Sons, New York.

[0071] Another embodiment of the process of the invention includes theoxidative dehydrogenation of an n-butene-containing mixture to give astream essentially consisting of butadiene and some yield of MAby-product. Of the mixture, which comprises butadiene and a little MA, asubstream is reacted in a second oxidation to give MA, the substreamratio being as desired for the reaction of step (1). That substream fromthe first reaction which has not been subjected to further reaction isreacted with the product stream from the second oxidation in thecondensed phase in step (1) to give the cyclohexenedicarboxylic acidanhydride. The discharge from the first oxidation reaction may be passedin gaseous form into the second oxidation, where it is further oxidized.Following the second oxidation, MA is then obtained as a crude solutionfrom the reaction effluent, by absorption in a high-boiling inertsolvent. The substream which comprises the gaseous butadiene which comesfrom the first oxidation and has not been subjected to further reactionmay then be introduced into the crude solution of MA in the high-boilingsolvent. The reaction of step (1) may be carried out directly with theresultant mixture of the crude products.

[0072] In particular, another embodiment of the invention provides aprocess for preparing a cyclohexanedicarboxylic acid or a derivativethereof, which proceeds by the following scheme (III):

[0073] wherein in scheme (III) E is n-butenes (raffinate), L is air, catA is catalyst system A, cat B is catalyst system B, and P iscyclohexane-1,2-dicarboxylic ester.

[0074] In another embodiment of the present invention, thebutadiene/maleic acid anhydride mixture is subjected to a treatmentprior to the reaction of step (1). An example of a treatment for thepurposes of the present invention is the removal of a by-product, or inparticular enrichment with one component in order to obtain astoichiometric ratio of the components suitable for the reaction of step(1).

[0075] According to the invention, however, it is equally possible forthe butadiene/maleic acid anhydride mixture not to be subjected to anytreatment prior to the reaction of step (1).

[0076] According to the invention, it is also possible for thebutadiene/maleic acid anhydride mixture for the reaction of step (1) tobe obtained from crude butadiene and crude maleic anhydride. For thepurposes of the present invention, crude butadiene and crude maleic acidanhydride are preferably streams which comprise at least 60% by weight,in particular at least 80% by weight, of butadiene and, respectively,maleic anhydride.

[0077] The in-situ preparation of butadiene and direct reaction in step(1) according to the invention can avoid the complicated use ofcontrolled-release depot compounds which release the dienes in thehomogeneous reaction medium used for the reaction, for example asdescribed in DE 1 082 908, which describes a case where the use of depotcompounds is needed to avoid using the pure form of dienes which readilypolymerize.

[0078] Within the framework of the present invention, dienes besidesbutadienes may be C5 dienes, i.e. dienes with 5 C atoms. Besides thepure C5 dienes, mixtures of various dienes may also be used. Inaccordance with the invention, e.g. a C5 cut is inserted into theDiels-Alder reaction as per step (1). The C5 cut is a mixture of variousC5 hydrocarbons, e.g. resulting from the cracking of hydrocarbons withlonger chains. The advantage of the use of the C5 cut is that atime-consuming and expensive purification of the individual C5 dienes isavoided. Thus, the present invention relates also in a preferredembodiment to a process for the production of an alkyl-substitutedcyclohexanedicarboxylic acid or a derivative thereof, wherein C5 cutsfrom a crack processes are used as C5 dienes.

[0079] In the Diels-Alder reaction with maleic acid anhydride (MA) asper step (1), merely the dienes cyclopentadiene, isoprene, andpiperylene, i.e. the conjugated dienes are those C5 hydrocarbons of theC5 cut which react. E.g. in the C5 cut of crackers, 5 to 30% by weight,preferably 10 to 25% by weight, in particular 15 to 20% by weight ofcyclopentadiene are contained, which can partially be present in theform of dicyclopentadiene, preferably 17% by weight, 5 to 25% by weightpreferably 10 to 20% by weight, in particular 12 to 18% by weightisoprene, preferably 15% by weight and approximately 5 to 25% by weight,preferably 10 to 20% by weight, in particular 8 to 12% by weightpiperylene, preferably 10% by weight. Moreover, the C5 cut may compriseother compounds, inert under the reaction conditions of the invention.The C5 cut may e.g. comprise n-pentane, i-pentane, i-pentene, 2-penteneor methylbutene, the sum of all components resulting in 100% by weight.

[0080] The Diels-Alder reaction between the C5 cut and MA is in theframework of the present invention performed thermally at temperaturesof 40 to 250° C. without pressure or under the reaction system's ownpressure in presence of radical polymerization inhibitors. If the C5 cutcontains dicyclopentadiene besides cyclopentadiene and this is alsomeant to react, a two-step method may be used in the Diels-Alderreaction in accordance with the invention. Therein, at first monomericdienes are reacted at a low temperature, e.g. between 40 and 140° C.with MA. Subsequently, the temperature is increased to 150 to 250° C. inorder to react dicyclopentadiene. In accordance with the invention,however, it is possible to perform the reaction discontinuously in areactor by step-wise increase of the temperature. However, in the sameway it is possible to perform the reaction continuously in a sequence ofreactors or reactor segments, operated at different temperatures.Appropriate reactors for the Diels-Alder reaction are e.g. stirringreactors or tubular reactors.

[0081] In accordance with the invention, it is also possible to performthe reaction of the C5 cut with MA in accordance with step (1) in such away that the cyclopentadiene present as dicyclopentadiene is notreacted. Therefor, the temperature is held at below 140° C. in theDiels-Alder reaction. Such a reaction process leads to the portion of5-norbonene-2,3-dicarboxylic acid anhydride in the product mixture beingreduced.

[0082] The C5 hydrocarbon atoms of the C5 cut which do not react withmaleic acid anhydride, can be easily separated after the reaction ofstep (1), e.g. by means of distillation.

[0083] In the reaction of the C5 cut as per step (1), a mixture ofvarious anhydrides is obtained. Mixtures of 5-norbonene-2,3-dicarboxylicacid anhydride (mixture of endo and exo compound),4-methyl-4-cyclohexene-1,2-dicarboxylic acid anhydride and3-methyl-4-cyclohexene-1,2-dicarboxylic acid anhydride are obtained.Therein e.g. 0 to 30% by weight, preferably 10 to 25% by weight,especially preferred 15 to 20% by weight 5-norbonene-2,3-dicarboxylicacid anhydride, preferably 17% by weight (mixture of endo and exocompound), 0 to 25% by weight, preferably 10 to 20% by weight, inparticular 12 to 18% by weight4-metyhl-4-cyclohexene-1,2-dicarboxyicacid anhydride, preferably 15% byweight, and 0 to 25% by weight, preferably 10 to 20% by weight, inparticular 8 to 12% by weight 3-methyl-4-cyclohexene-1,2-dicarboxylicacid anhydride, preferably 10% by weight are present in the mixture.

[0084] In accordance with the invention it is possible to subject amixture of an alkyl-substituted cyclohexenedicarboxylic acid anhydrideresulting from step (1) via the reaction of MA and at least one C5 dieneto a treatment. Within the framework of the present invention, themixtures obtained as per step (1) by reaction of MA and at least one C5diene can thus be further reacted directly or be separated into the purecompounds e.g. by a distillative process. It is possible in accordancewith the invention to perform the subsequent reactions with the purecompounds. It is also possible to further react the mixture obtained inthe reaction as per step (1).

[0085] In the following, explanations regarding cyclohexene orcyclohexanedicarboxylic acid derivatives refer to the alkyl-substitutedas well as unsubstituted dicarboxylic acid derivatives or to themixtures obtained in step (1).

[0086] According to the invention, the cyclohexenedicarboxylic acidanhydride obtained in step (1) may then be purified or be reacteddirectly in the form of a crude solution.

[0087] For the purposes of the present invention, the resultant crudesolution of cyclohexenedicarboxylic acid anhydride may be esterified instep (2) to give the cyclohexenedicarboxylic ester. The formation of theester here may take place by esterification with an alcohol with analkyl-, cycloalkyl- or alkoxyalkyl-residue or with a mixture of two ormore thereof wherein the alkyl-, cycloalkyl-, as well asalkoxyalkyl-groups contain generally 1 to 30, preferably 2 to 20 andparticularly preferably 3 to 18 carbon atoms and may be branched orlinear. In particular, the reaction is performed with linear orbranched, saturated alcohols having from 1 to 20 carbon atoms, or usinga mixture of two alcohols of this type. The reaction is carried out inthe manner known to a skilled worker, as described by way of example inOrganikum, 18th edition, 1990, Deutscher Verlag der Wissenschaften,Berlin.

[0088] In accordance with the invention, the esterification may inparticular be performed with linear and branched alcohols with 1 to 18 Catoms, preferably 4 to 13 C atoms, particularly preferably 8 to 10 Catoms. Alcohols may be methanol, ethanol, linear or branched propanols,linear or branched butanols, linear or branched pentanols, linear orbranched hexanols, linear or branched heptanols, linear or branchedoctanols, linear or branched nonanols, linear or branched decanols,linear or branched undecanols, linear or branched dodecanols, linear orbranched tridecanols, linear or branched tetradecanols, linear orbranched pentadecanols, linear or branched hexadecanols, linear orbranched heptadecanols, linear or branched octadecanols, as well asmixtures of these alcohols.

[0089] The alcohols may be e.g. oxoaclohols, hydroformulation productsof C5 to C12 alkenes and hydroformulation products of dimer-, trimer-and oligomer-ethene, of dimer-, trimer- and oligomer-propene, of dimer-,trimer- and oligomer-n- or -i-butene, of dimer-, trimer- and oligomer-n-or -i -pentene and of dimer-, trimer- and oligomer-n- or -i -hexene.

[0090] Particularly useful are e.g. hexanol mixtures with the ChemicalAbstracts Number (in the following CAS no.) 68526-79-4, heptanolmixtures with the CAS no. 51774-11-9, octanol mixtures with the CAS no.68526-83-0, octanol mixtures with the CAS no. 91994-92-2,2-ethyl-hexanol, nonanol mixtures with the CAS no. 68526-84-1, nonanolmixtures with the CAS no. 3452-97-9, nonanol mixtures with the CAS no.27458-94-2, decanol mixtures with the CAS no. 93821-11-5, decanolmixtures with the CAS no. 25339-17-7, 2 propylheptanol undecanolmixtures with the CAS no. 90604-37-8, dodecanol mixtures with the CASno. 90604-37-8, tridecanol mixtures with the CAS no. 27458-92-0 andtridecanol mixtures with the CAS no. 68526-86-3.

[0091] In an alternate embodiment of the invention, the formation of theester in step (2) may take place by dimerizing dienes on thecyclohexenedicarboxylic acid anhydride itself. This gives esters havingC8 side chains. This provides a useful means of utilizing the butadienefrom the prior oxidation of raffinate for this part of the process too.FR 15 79 244 and JP 50-005737 describe suitable conditions for thereaction to build up the ester side chain by way of butadienedimerization.

[0092] For the purposes of the invention, it is also possible that theformation of the ester in step (2) takes place by an addition reactionof dienes on the cyclohexanedicarboxylic acid anhydride itself, or onthe corresponding carboxylic acid. This process permits in particularthe preparation of esters having C4 side chains.

[0093] The hydrogenation of the cyclohexene ring in step (3) mayadvantageously take place here together with the hydrogenation of theunsaturated side chain, in a single step of the reaction. Thecorresponding cyclohexane dialkyl ester is then obtained as a product ofthe reaction.

[0094] The hydrogenation of step (3) preferably takes place in thepresence of a catalyst, using a hydrogen-containing gas. Examples ofsuitable catalysts are platinum or palladium catalysts bound to poroussupport materials. Other conditions of the hydrogenation reaction ofstep (3) are given by way of example in Organikum, 18th edition, 1990,Deutscher Verlag der Wissenschaften, Berlin. For the hydrogenation ofthe invention, fixed-bed catalysts, suspension catalyst and homogeneoushydrogenation catalysts may be used, e.g. described in Houben-Weyl“Methods of organic chemistry”, Volume 4/1c. The hydrogenation can beeffected with normal pressure or increased pressure at temperatures from20° C. to 250° C. depending on the catalyst.

[0095] Other hydrogenation catalysts also particularly suitable for thepurposes of the invention are those mentioned in WO 99/32427 and DE-A199 27 978.0.

[0096] For the purposes of another preferred embodiment of theinvention, it is also possible, following step (1), to begin withhydrogenation of the cyclohexenedicarboxylic acid anhydride to givecyclohexanedicarboxylic acid anhydride in step (3). According to theinvention, the formation of the ester in step (2) as described abovethen gives the cyclohexanedicarboxylic ester.

[0097] With the method of the invention it is possible on the one handto produce pure compounds, on the other hand, mixtures of variousalkyl-substituted cyclohexane dicarboxylic acids or derivatives thereofmay be produced. In particular when using a mixture of more than one C5dienes for the reaction of step (1) it is possible to produce the purecompounds by means of a separation step at an arbitrary location in theproduction process, e.g. by distillation. It is, however, also possibleto perform the process without a separation step and thus to obtainmixtures of various alkyl-substituted cyclohexanedicarboxylic acids orderivatives thereof.

[0098] In particular it is possible with the method of the invention toproduce nobonan-2,3-dicarboxylic acid,4-methylcyclohexane-1,2-dicarboxylic acid and3-methylcyclohexane-1,2-dicarboxylic acid or derivatives thereof as purecompounds, i.e. with a content of >90% by weight. In the same way,mixtures comprising 0 to 70% by weight, preferably 10 to 65% by weight,in particular 15 to 60% by weight, particularly preferably 20 to 55% byweight nornbonan-2,3-dicarboxylic acid or a derivative thereof, 0 to 70%by weight, preferably 10 to 65% by weight, in particular 15 to 60% byweight, particularly preferably 20 to 55% by weight4-methylcyclohexane-1,2-dicarboxylic acid or a derivative thereof and 0to 70% by weight, preferably 10 to 65% by weight, in particular 15 to60% by weight, particularly preferred 20 to 55% by weight3-methylcyclohexane-1,2-dicarboxylic acid or derivatives thereof areproduced with the method of the invention, wherein the sum of theindividual elements of the mixture results in 100% by weight.

[0099] Therefore, the invention also relates to alkyl-substituted orunsubstituted cyclohexanedicarboxylic acids or derivatives thereof,obtainable by a process, comprising the following steps (1) to (3):

[0100] (1) Converting a diene/maleic acid anhydride mixture to give analkyl-substituted or unsubstituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0101] (2) Forming an ester from the alkyl-substituted or unsubstitutedcyclohexenedicarboxylic acid anhydride;

[0102] (3) Hydrogenation of the alkyl-substituted or unsubstitutedcyclohexene derivative of step (2) to give the corresponding cyclohexanederivative;

[0103] or

[0104] (1) Converting a diene/maleic acid anhydride mixture to give analkyl-substituted or unsubstituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0105] (3) Hydrogenation of the alkyl-substituted or unsubstitutedcyclohexenedicarboxylic acid anhydride to give cyclohexanedicarboxylicacid anhydride;

[0106] (2) Forming an ester from the alkyl-substituted or unsubstitutedcyclohexanedicarboxylic acid anhydride.

[0107] In another embodiment, the invention relates to alkyl substitutedor unsubstituted cyclohexane dicarboxylic acids or derivatives thereof,obtainable by a process, comprising the following steps (1) to (3):

[0108] (1) Converting a butadiene/maleic acid anhydride mixture to givea cyclohexenedicarboxylic acid anhydride in the condensed phase;

[0109] (2) Forming an ester from the cyclohexenedicarboxylic acidanhydride;

[0110] (3) Hydrogenation of the cyclohexene derivative of step (2) togive the corresponding cyclohexane derivative;

[0111] or

[0112] (1) Converting a butadiene/maleic acid anhydride mixture to givea cyclohexenedicarboxylic acid anhydride in the condensed phase;

[0113] (3) Hydrogenation of the cyclohexenedicarboxylic acid anhydrideto give cyclohexanedicarboxylic acid anhydride;

[0114] (2) Forming an ester from the cyclohexanedicarboxylic acidanhydride.

[0115] In another preferred embodiment, the invention relates toalkyl-substituted cyclohexanedicarboxylic acids or derivatives thereof,obtainable by a process, comprising the following steps (1) to (3):

[0116] (1) Converting a mixture of maleic acid anhydride and at leastone C5 diene to give an alkyl-substituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0117] (2) Forming an ester from an alkyl-substitutedcyclohexenedicarboxylic acid anhydride;

[0118] (3) Hydrogenation of the alkyl-substituted cyclohexene derivativeof step (2) to give the corresponding cyclohexane derivative;

[0119] or

[0120] (1) Converting a mixture of maleic acid anhydride and at leastone C5 diene to give an alkyl-substituted cyclohexenedicarboxylic acidanhydride in the condensed phase;

[0121] (3) Hydrogenation of the alkyl-substitutedcyclohexenedicarboxylic acid anhydride to give cyclohexanedicarboxylicacid anhydride;

[0122] (2) Forming an ester from the alkyl-substitutedcyclohexanedicarboxylic acid anhydride.

[0123] Moreover, the present invention also relates to mixtures,comprising at least one alkyl-substituted or unsubstitutedcyclohexanedicarboxylic acid or a derivative thereof.

[0124] In particular, the invention relates to mixtures comprising atleast norbonan-2,3-dicarboxylic acid,4-methylcyclohexane-1,2-dicarboxylic acid and3-methylcyclohexane-1,2-dicarboxylic acid or derivatives thereof. Suchmixtures have e.g. particularly advantageous properties for the use asplasticizer.

[0125] Particularly appropriate are therein the isononyl esters or2-ethylhexyl esters of the respective cyclohexane dicarboxylic acid,wherein the isononanol used for producing the ester has the CAS number27458-94-2. Thus, the present invention relates in another embodiment tomixtures comprising 0 to 70% by weight norbonan-2,3-dicarboxylicacid-bis-(2-ethylhexyl)ester, 2 to 70% by weight4-methylcyclohexane-1,2-dicarboxylic acid-bis-(2-ethylheyl)ester and 2to 70% by weight 3-methylcyclohexane-1,2-dicarboxylicacid-bis-(2-ethylhexyl)ester as well as mixtures comprising 0 to 70% byweight norbonan-2,3-dicarboxylic acid-bis-(isononyl)ester, 2 to 70% byweight 4-methylcyclohexane-1,2-dicarboxylic acid-bis-(isononyl)ester and2 to 70% by weight 3-methylcyclohexane-1,2-dicarboxylciacid-bis-(isononyl)ester.

[0126] The invention further provides the use of an alkyl-substituted orunsubstituted cyclohexanedicarboxylic acid according to the invention ora derivative thereof or of a mixture comprising suchcyclohexanedicarboxylic acid or a derivative thereof as plasticizers forplastics, in particular polyvinylchloride (PVC) or polyvinylbutyral(PVB).

[0127] The proportions of the cyclohexanedicarboxylic acids preparedaccording to the invention, or a derivative thereof, added to theplastics are from 1 to 80% by weight, preferably from 5 to 55% byweight, particularly preferably from 10 to 50% by weight and inparticular from 15 to 45% by weight.

[0128] For the purposes of the present invention, a plasticizer is asubstance whose addition reduces the hardness of the plastic.

[0129] The esters of the invention have a low density and viscosity. Thelow density leads to advantageous volume costs of the plastics producedwith the inventive plasticizers. The low viscosity improves theprocessing behavior when producing dry blends and leads to lower initialplastisol viscosities when producing pastes.

[0130] Moreover, the plasticizers in accordance with the invention causean improvement of the cold-elastic properties of the plastics made withthese plasticizers and an increased thermostability. Thecharacterization of the cold-elastic properties is effected preferablyby means of the so-called coldness-breaking temperature. This is thetemperature at which a plastic shows first optically visible damages inthe cold when mechanically acted upon. The determination of thecoldness-breaking temperature is effected in accordance with DIN 53372.The characterization of the thermal stability is effected e.g. with PVCby means of the co-called HCl remaining stability. This is the intervalduring which plasticized PVC shows no decomposition connected with HClformation at a temperature of 200° C. The determination of the HClremaining stability is effected in accordance with VDE standard 0472,§614.

[0131] The cyclohexanedicarboxylic acids prepared according to theinvention, or a derivative thereof, may also be used as plasticizer formixtures of various plastics, for example of polyvinyl chloride orpolyvinyl butyral with other plastics selected from the group consistingof homo- and copolymers based on ethylene, propylene, butadiene, vinylacetate, glycidyl acrylate, glycidyl methacrylate, or of acrylates ormethacrylates having alcohol components of branched or unbranched C1-C10alcohols, styrene, or acrylonitrile.

[0132] Examples of the uses of the plastics plasticized with thecyclohexanedicarboxylic acids prepared according to the invention, orwith a derivative thereof, include cases for electrical devices, such askitchen machines or computers, piping, chemical engineering, cables,wire sheathing, window profiles, interior fittings, vehicleconstruction, furniture construction, floor coverings, production ofgaskets, films, composite films, films for laminated safety glass, inparticular TROSIFOL grade PVB films from HT-Troplast, phonographicdisks, synthetic leather, toys, packaging containers, adhesive tapefilms, clothing, coatings, and fibers for fabrics.

[0133] In the following the present invention is illustrated with someexamples.

EXAMPLES Example 1 Diels-Alder Reaction of a C5 Cut with Maleic AcidAnhydride

[0134] A mixture of 98 g maleic acid anhydride (1.0 mole) and 180 g CS5cut with a content of 17% by weight cyclopentadiene (present as amixture of approximately 2% by weight cyclopentadiene and approximately15% by weight dicyclopentadiene), approximately 15% by weight isopreneand approximately 10% by weight piperylene was heated with 1000 ppmphenothiacine as radical inhibitor in an autoclave for initially 3 hoursup to 70° C. and then for 5 hours up to 180° C. Subsequently, the notreacted hydrocarbons were distilled at normal pressure, finally in avacuum. A mixture of the following dicarboxylic acid anhydridesresulted: approximately 35% 5-norbonene-2,3-carboxylic acid anhydride(mixture of endo and exo compounds), approximately 39%4-methyl-4-cyclohexene-1,2-dicarboxylic acid anhydride and approximately26% 3-methyl-4-cyclohexen-1,2-dicarboxylic acid anhydride.

Example 2 Hydrogenation

[0135] 110 g of the reaction mixture from example 1 were dissolved in400 ml THF. Subsequently 300 mg palladium on activated carbon (10% Pd)were added and hydrogenated at room temperature at 100 bar hydrogenpressure. The catalyst was then filtered off and the solvent wasdistilled off in a rotation evaporator. 112 g of a mixture ofapproximately 35% 5-norbonan-2,3-dicarboxylic acid anhydride,approximately 39% 4-methyl-4-cyclohexane-1,2-dicarboxylic acid anhydrideand approximately 26% 3-methyl-4-cyclohexane-1,2-dicarboxylic acidanhydride were obtained.

Example 3 Esterification

[0136] 106 g of the reaction mixture from example 2 were cooked with 250g 2-ethylhexanol and 0.16 g titanium tetrabutylat as catalyst on a watersedimentant until no water was formed any longer. Then, the catalyst washydrolyzed with a soda solution (content 0.5%), the water phase wasseparated and the organic phase was again washed with water. Finally,the excessive ethylhexanol was distilled off, wherein the last remainingalcohol was removed by stripping with vapor. 166 g of a mixture ofapproximately 35% 5-norbonan-2,3-dicarboxylicacid-bis-(2-ethylhexyl)ester, approximately 39%4-methyl-4-cyclohexane-1,2-dicarboxylic acid-bis-(2-ethylhexyl)ester andapproximately 26% 3-methyl-4-cyclohexane-1,2-dicarboxylicacid-bis-(2-ethylhexyl)ester were obtained.

Examples 4 and 5

[0137] Analogously to example 3, the esterification was performed withisononanol and 2-propylheptanol. Corresponding ester mixtures wereobtained.

We claim:
 1. A process for preparing an alkyl-substituted orunsubstituted cyclohexane-dicarboxylic acid, mono- or diesters or oranhydrides thereof, comprising the following sequences of steps (1) to(3): (1) Converting a diene/maleic acid anhydride mixture to givealkyl-substituted or unsubstituted cyclohexenedicarboxylic acidanhydride in the condensed phase; (2) Forming an ester from analkyl-substituted or unsubstituted cyclohexenedicarboxylic acidanhydride; (3) Hydrogenation of the alkyl-substituted or unsubstitutedcyclohexene derivative of step (2) to give the corresponding derivativeof cyclohexane; or (1) Converting a diene/maleic acid anhydride mixtureto give an alkyl-substituted or unsubstituted cyclohexenedicarboxylicacid anhydride in the condensed phase; (3) Hydrogenation of thealkyl-substituted or unsubstituted cyclohexenedicarboxylic acidanhydride to give cyclohexanedicarboxylic acid anhydride; (2) Forming anester from the alkyl-substituted or unsubstitutedcyclohexanedicarboxylic acid anhydride.
 2. A process for preparing acyclohexanedicarboxylic acid, mono- or diesters or anhydrides thereof,as claimed in claim 1 comprising the following sequence of steps (1) to(3): (1) Converting a butadiene/maleic acid anhydride mixture to givecyclohexenedicarboxylic acid anhydride in the condensed phase; (2)Forming an ester from a cyclohexenedicarboxylic acid anhydride; (3)Hydrogenation of the cyclohexene derivative of step (2) to give thecorresponding derivative of cyclohexane; or (1) Converting abutadiene/maleic acid anhydride mixture to give acyclohexenedicarboxylic acid anhydride in the condensed phase; (3)Hydrogenation of the cyclohexenedicarboxylic acid anhydride to givecyclohexanedicarboxylic acid anhydride; (2) Forming an ester from thecyclohexanedicarboxylic acid anhydride.
 3. A process for preparing acyclohexanedicarboxylic acid, mono- or diesters or anhydrides thereof,as claimed in claim 1 or 2, wherein the butadiene/maleic acid anhydridemixture for the reaction according to step (1) is obtained by a processcomprising the oxidation of flows containing n-butene or butadiene or amixture thereof or by a process comprising the oxidation of n-butene togive butadiene or by a process comprising the oxidation of n-butene togive a butadiene/maleic acid anhydride mixture.
 4. A process forpreparing a cyclohexanedicarboxylic acid, mono- or diesters oranhydrides thereof, as claimed in claim 3, wherein the n-butene toprepare the butadiene/maleic acid anhydride mixture for the reactionaccording to step (1) is obtained by a process comprising the oxidationof streams comprising n-butane.
 5. A process for preparing analkyl-substituted cyclohexanedicarboxylic acid, mono- or diesters oranhydrides thereof, as claimed in claim 1, comprising the followingsequences of steps (1) to (3): (1) Converting a mixture of maleic acidanhydride and at least one C5 diene to give alkyl-substitutedcyclohexenedicarboxylic acid anhydride in the condensed phase; (2)Forming an ester from an alkyl-substituted cyclohexenedicarboxylic acidanhydride; (3) Hydrogenation of the alkyl-substituted cyclohexenederivative of step (2) to give the corresponding derivative ofcyclohexane; or (1) Converting a mixture of maleic acid anhydride and atleast one C5 diene to give an alkyl-substituted cyclohexenedicarboxylicacid anhydride in the condensed phase; (3) Hydrogenation of thealkyl-substituted cyclohexenedicarboxylic acid anhydride to givecyclohexanedicarboxylic acid anhydride; (2) Forming an ester from thealkyl-substituted cyclohexanedicarboxylic acid anhydride.
 6. A processas claimed in claim 5, characterized in that C5 cuts from a crackprocess are used as C5 diene.
 7. Mixture, comprising at least onealkyl-substituted or unsubstituted cyclohexanedicarboxylic acid or aderivative thereof, obtainable in accordance with a process as claimedin any one of the claims 1 to 6, wherein at leastnorbonan-2,3-dicarboxylic acid, 4-methylcyclohexane-1,2-dicarboxylicacid and 3-methylcyclohexane-1,2-dicarboxylic acid or a derivative ofthese carboxylic acids are comprised.
 8. The use of an alkyl-substitutedor unsubstituted cyclohexanedicarboxylic acid, mono- or diesters oranhydrides thereof, prepared by a process as claimed in any of claims 1to 6, or a mixture as claimed in claim 7 as a plasticizer for plastic,wherein the plastic is polyvinyl chloride or polyvinyl butyral.